The present invention relates to the use of very low friction material formed into patches or pieces and adhered to the skin or to a surface in contact with the skin (or immediately adjacent material such as a sock) to lower the magnitude of tangential traction of the surface in contact with the skin. The material reduces the likelihood of abrasion, trauma and ulceration in localized areas.
In the prior art, there have been efforts to reduce the co-efficient of friction of materials in load bearing contact with the skin, such as the surface of a lining of a shoe, which slides against a stocking. Also the regions where a limb prosthesis is in load bearing contact with a residual limb have been extensively considered for ways of reducing problems. The co-efficient of friction of smooth leather varies, depending on the moisture content, and when it gets wet can be quite high in friction. Moleskin patches have been sold and used for covering corns on the feet, as well as covering calluses, but this also has a relatively high co-efficient of friction against the inner surface of a shoe and the co-efficient of friction increases substantially when the moleskin is wet.
Blisters, abrasions, calluses, bursas and even some forms of sub-cutaneous tissue trauma are the result of applications of a combination of forceful contact and tangential tractions to the skin (forceful rubbing/forceful shearing). High shear stresses may cause damage in a single cycle. Low shear stresses may cause tissue damage when the number of cycles is great.
Tangential skin tractions relate directly to tissue shear stress and shear strain magnitudes. Shear strain is by its very nature very distortional and, when it exceeds certain levels, results in the tearing of biological tissues such as blood capillaries and interface (skin-subcutaneous) layers. High normal pressures (perpendicular to the skin surface) in the absence of significant tangential tractions are surprisingly well tolerated by skin and underlying tissue, especially when applications are of a short enough duration to avoid ischemic trauma (cell death after an extended period of blood flow blockage).
This invention is primarily aimed at reducing and preventing shear trauma from many repetitions of short duration skin loadings, but eliminating shear tractions even in low repetition, long-duration loadings is of value. Research shows that even capillary blood flow is affected strongly by whether or not shear stresses are superimposed on normal pressures. When high shear stresses are present, capillary blood flow has been shown to be occluded at normal pressures only half as great as what are required to occlude flow in the absence of shear stresses and strains.
There is some recognition among medical researchers and care-givers that shear plays a role in tissue trauma. However, how and when excessive shear stresses/strains occur and how they damage tissue are hard to visualize. Injury from a normal force (a simple, yet forceful, blow or bump causing injury by crushing tissue) is easier for people to visualize and understand. Shear stresses and how they vary over a given area (and vary with time) are very hard to measure; much harder than it is to measure normal pressure. In addition to the visualization and measurement difficulties just mentioned, there is the fact that few people have better than a vague qualitative awareness of how something called the xe2x80x9ccoefficient of frictionxe2x80x9d (C.F.) relates to blisters, abrasions, and calluses. Tangential traction force magnitudes can be no greater than the C.F. times the magnitude of normal force. Therefore, the simplest, most direct way to reduce shear induced tissue trauma is to choose materials which minimize friction against the at-risk skin surface areas. Until the present invention, there has been little practical awareness of, and attention given to, friction management.
Examination and knowledge of products on the market indicate that the opportunities for reducing callusing, blistering and abrasions by friction management has been almost entirely unappreciated by designers of shoes, orthoses, prostheses, and many other objects that come in repeated or prolonged contact with the human body.
Thin silk or synthetic fiber sheets have been used by amputees to pull over their residual limbs before pulling on a cotton or wool sock and then donning the limb prosthesis. The co-efficient of friction between the sheet and the sock is reduced under dry conditions and does protect the residual limb to some extent from friction and consequent shear-related trauma. The coefficient of friction increases substantially when the material becomes damp or wet. In most cases, the material used to line shoes and prosthetic sockets, for example, represent high friction choices. Foam products are used to line prosthetic sockets, orthoses, and shoe insoles and represent a particularly poor material from the standpoint of friction management. Damp skin and sock material literally sticks to such foams.
Synthetic gel socket liners are available, and these are generally in the range of xe2x85x9 inch {fraction (5/16)} inch thick. The liner cover tends to stick to the skin and other materials in contact with it, so that it does not act as a friction reducer, but does provide cushioning and accommodates small amplitude shear motions without much resistance. The effectiveness of a gel liner is dependent on its thickness, and as it becomes thicker, its weight and bulk are deterrents.
Thus, the concept of providing a very low friction interface between the skin and surfaces that contact the skin, particularly in high load and high shear areas, has escaped the workers in the field and the need exists for reduction of trauma to the skin where the skin and tissue are supported.
The present invention relates to providing a layer of material that has a very low friction outer surface in both dry and wet conditions to provide an interface with a surface that normally would support the skin either directly or through a cloth covering, such as a sock fabric. In the usual situation, the surface loading or bearing on the skin may be the inner surface of an orthosis, the socket surface of a prosthesis, or inner surfaces of a shoe, especially insoles, but also other inner surfaces. The layer of low-friction material is adhered, preferably, to the surface of the object that bears on the skin and faces the skin, although applying the layer with an adhesive directly on the skin in the affected area with the low friction surface facing the support is also contemplated. The purpose of the low friction material is to lower the magnitude of tangential tractions that the surface of the object can exert against the skin.
The use of intervening layers is contemplated in the present invention, so a sock or sheet placed between the low friction pad and the skin does not adversely affect the performance.
A low friction surface layer used may be on material in the form of a sheet, or a small patch that is pre-cut, or custom cut to a desired size, and having a pressure sensitive adhesive on the surface of the patch opposite from the low friction surface. The adhesive may be on the outer surface of another layer of material, such as a foam backing cushion layer or a stretch fabric backing bonded to the low friction material. A release paper is placed on the exposed adhesive. When the release paper is removed, the patch or piece of material providing the low friction surface layer can be adhered into a certain desired position of the surface of the skin or on the object that bears on the skin.
Made of polytetrafluoroethylene (PTFE). The PTFE layer is preferably bonded to a fabric layer of a somewhat elastic, flexible material such as Lycra or a Lycra blend. The exposed side of the fabric is covered with a pressure adhesive and a release paper is on top of the adhesive.
The thin sheet of PTFE material can be used without any backing sheets by applying adhesive directly to the PTFE layer. Bonding a very thin sheet of PTFE to a stretch fabric without having the PTFE separate from the fabric during use gives the desired low friction characteristics of the outer surface, while permitting the formed patch to conform to irregular shapes or surfaces, because of the stretch fabric underneath the thin layer of PTFE. The stretch fabric also gives the thin layer of low friction material, such as PTFE, xe2x80x9cbodyxe2x80x9d so it can be handled reasonably during the release paper stripping and application of the layer or patch to the desired surface. Very thin layers of PTFE tend to wrinkle or fold and cause problems with getting them very smooth. The elasticity of the backing fabric allows conformance into recesses, over convexities, and onto a combination of compound contoured surfaces.
Cushioning material,such as foam can be placed between the patch and the surface supporting the patch, if desired, to provide a cushioning effect, as is known. Various shapes can be made, including shapes which would have the stretch fabric toward the center of the patch or piece so that it was surrounded by an adhesive coated thin low friction material.
A preferred method of use includes placement of suitable size pieces or patches of the low friction coefficient material either on the skin or on the surface that will be next to the skin in locations where shear trauma is likely to occur. These patches or pieces can be held in place with suitable adhesive on the back side of the low friction material. Foam or other compressible material for cushioning can be used wherever needed.
Another aspect or form of the protective patch is the PTFE film or layer bonded to a calf skin leather hide, textile foam liner, or other material that could be used to line the inner wall of the toe box of a shoe. The composite material can be sewn and applied in the same manner as the lining material now is applied without a PTFE film surface. The usefulness of this material is realized in its ability to shield dorsal and peripheral surfaces of the foot from damaging shear forces. At these non-plantar locations, high tangential tractions can be present, but more often trauma develops from lower forces, that generate excessive callus/corn growth and/or tissue breakdown by the action of cyclic (high frequency) loading.
The patches of the present invention offers an easy way to accomplish xe2x80x9cfriction managementxe2x80x9d. The surfaces that a shoe, orthosis, or prosthesis present to the skin vary as to their function and as to the tissue trauma risk they present. It is also true that some areas of the anatomy within a shoe, prosthesis, or orthoses are at greater or lesser risk because of the level of peak forces and/or the amount of soft tissue interposed between skin and bone. Some parts of an orthosis bear only slightly or not at all against the corresponding skin surface. Other parts bear very firmly in order to provide maximum orthopedic support, correction, or weight bearing. Still other surfaces such as the supra-condylar parts of a BK (lower leg) prosthesis socket serve to suspend (during swing-through) or maintain position of the device.
All of these just-noted facts are important because they are reasons to vary the friction coefficient depending on the surface function. For instance, there is very little reason to be concerned about the friction coefficient of a surface in only very light contact with the skin (unless the number of repetitions is very high). Forceful cyclical contact against a skin surface is a situation that benefits more from minimizing the friction coefficient. If the area is xe2x80x9cbonyxe2x80x9d minimizing friction becomes more important.
In a case like the supra-condylar suspension areas of the BK socket mentioned earlier, high friction (even xe2x80x9cstickyxe2x80x9d) materials may be desired. Applying the low friction patches of an aspect of the invention to certain areas and not others is a way to add friction management to the orthotist""s (prosthetist""s, podiatrist""s, etc.) treatment methods and appliances. In cases where the professional wishes to apply maximum supportive/corrective pressure the near elimination of friction and shear in selected regions means that much greater support can be safely provided without approaching tissue trauma conditions.
There are also many consumer (nonprofessional) applications for the present invention. Many people are plagued by excessive callus build-up. A person with excessive calluses under the metatarsal heads might remove the shoe insoles and apply low friction patches to the corresponding surface of the insole. If the excessive callus is in the form of xe2x80x9ccornsxe2x80x9d the person could apply a low friction corn pad to relieve some pressure on a painful corn (by means of annular cushioning material) and greatly reduce the friction and shear which originally generated, and then maintains the corn callus.
A similar but much larger patch might be applied by a skater over ankle bones to allow tight (er) lacing with greater comfort and less chance of trauma at the apices of those bony prominences. As an alternative, the skater may choose to adhere the patch to the appropriate locations on the inside surface of the skate uppers. There are a myriad of other possibilities such as on kneeling pads (for cement workers, etc.) or on backpack shoulder straps.
A similar (but non-consumer) use of the cushioned patch (continuous, annular, or donut types) is in hospitals for prevention of bed sores. Low friction cushion patches of the present invention applied over healthy bony areas such as sacrum-coccyx, greater trochanter, heels, and elbows as a prophylactic measure act to inhibit the generation of bed sores.